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In search of efficient technologies to reduce CO₂ emissions, researcher from around the world come up with the most astonishing ideas to create devices or materials to convert exhaust gases in power plants to electricity and other useful products. To do so, different approaches have been tried and tested. One of them consists in integrating 3D printing into materials science to create a new superalloy. 3D printing uses a high-power laser to flash-melt a material, usually a plastic or a metal and then deposits that material in layers to build a new object.

Now (2023), with the help of a 3D printer scientists at Sandia Lab created a high-performance metal alloy which had an unusual composition making it stronger and lighter than the commonly-used materials in gas turbine machinery. These findings could have a huge impact in many industries, including the energy sector as well as the aerospace and automotive industries.

The new superalloy consisted of 42% aluminum, 25% titanium, 13% niobium, 8% zirconium, 8% molybdenum and 4% tantalum and was stronger at 800 degrees Celsius than many other high-performance alloys, including those currently used in turbine parts. It was still stronger when it cooled down to room temperature. The alloy exhibited minor softening up to 800°C and consisted of four compositionally distinct phases. Density functional theory calculations showed that there was a thermodynamic explanation for the observed temperature-independent hardness and favourability for the formation of this multiplicity of phases.

The scientists made use of the many benefits of 3D printing and melted together powdered metals and then immediately print a sample of it. Their material is a fundamental shift in alloy development because each of its constituents makes up only a part of the whole alloy, which did not use to be common formerly. However, the scientists want to go even further: ““We have a lot of examples of where we have combined two or three elements to make a useful engineering alloy. Now, we’re starting to go into four or five or beyond within a single material. And that’s when it really starts to get interesting and challenging from materials science and metallurgical perspectives.”

Image: HAADF STEM images showing (A, B) grain and phase structure, (C) evidence of high coherence at phase 3/4 interfaces, and (D-E) lattice structures of phases 1 and 2 with overlaid elemental composition relative intensity maps, which indicate partial chemical ordering for phases 1 and 2, and (F, G) lattice structures of phases 3 and 4 along with inset FFT patterns. The lattice constant for phase 4, a BCC solid solution, matched the DFT predicted value



Source: Andrew B. Kustas, Morgan R. Jones, Frank W. DelRio, Ping Lu, Jonathan Pegues, Prashant Singh, A.V. Smirnov, Jordan Tiarks, Eric D. Hintsala, Douglas D. Stauffer, Jessica K. Romban-Kustas, Michael Abere, Emma M.H. White, Duane D. Johnson, Iver E. Anderson, Nicolas Argibay/ Extreme hardness at high temperature with a lightweight additively manufactured multi-principal element superalloy/ Applied Materials Today Volume 29, December 2022/ doi.org/10.1016/j.apmt.2022.101669/ Open Source This is an Open Access article is distributed under the terms of the Attribution 4.0 International (CC BY 4.0)

Improving materials has long been a chief interest of materials science. In 2020, scientists investigated high temperature cyclic oxidation on 800H superalloy, composed of Fe-33Ni-19Cr alloy at 700℃ for 150 cycles in laboratory air. Two types of samples were used: The Fe-33Ni-19Cr alloy was subjected to different heat treatment temperatures ranging from 1000℃ to 1100℃. The alloy experienced a short oxidation period at 700℃ for one hour, followed by cooling for 20 minutes for each cycle. The oxide phase analysis was performed using x-ray diffraction (XRD) technique. The cross-sectional line scan analysis was carried out with the help of a field emission scanning electron microscope (FESEM) equipped with an energy dispersive x-ray (EDX) spectrometer. The phase analysis found that four types of structure formed on the oxidized sample, consisting of austenite phase contained in the base metal, corundum oxides, spinel oxides and fluorite oxides structure. The cross-sectional analysis indicated that the oxidized samples formed a several oxide layers, mainly composed of Cr-Mn and Cr-Ti rich oxide.

Image: Cross sectional FESEM image with corresponding EDX line scan analysis of oxidized Fe-33Ni-19Cr alloy after 150 cycles: (a) H10 and (b) H11



Source: Noraziana Parimin, Esah Hamzah/ High Temperature Cyclic Oxidation of Ni-based 800H Superalloy at 700°C in Air/ IOP Conference Series Materials Science and Engineering 957(1):012013, November 2020/ DOI:10.1088/1757-899X/957/1/012013/ Open Source This is an Open Access article is distributed under the terms of the Attribution 3.0 Unported (CC BY 3.0)

In 2022, a quantitative characterization of precipitates and oxide inclusions in Inconel 625, coomonly found in energy, aviation, automotive and chemical industries, for  additively manufactured by the laser powder-bed fusion (L-PBF) process was performed. Through application of different microscopy techniques allowed the microstructure at micro- and nano-scale was characterized and the features of grains and cellular substructure was correlated with parameters of particles along the planes parallel and perpendicular to the build direction. This allowed easy distinguishing precipitates and oxide inclusions and performing their quantitative analysis. The results showed that intercellular areas are the preferential sites of precipitation of the intermetallic phases and NbC carbides with diameters in the range of 10 to 440 nm. The analysis provided detailed information about the parameters of particles depending on the orientation versus the build direction. It was demonstrated that despite the tendency for columnar grain morphology and the anisotropy of the cellular substructure, the particle distribution is almost uniform throughout the volume of the additively manufactured L-PBF Inconel 625.

Image: SEM images of the cellular substructure with exemplary precipitates marked: (a, b) as-built and (c, d) stress-relief annealed sample, as well as (e, f) size distributions of precipitates observed in SEM SE images in both xz and xy planes



Source: Sylwia Staroń, B. Dubiel, Kewin Gola, Izabela Kalemba-Rec/ Quantitative Microstructural Characterization of Precipitates and Oxide Inclusions in Inconel 625 Superalloy Additively Manufactured by L-PBF Method/ Metallurgical and Materials Transactions A 53(7), May 2022/ DOI:10.1007/s11661-022-06679-1/ Open Source This is an Open Access article is distributed under the terms of the Attribution 4.0 International (CC BY 4.0)

There are several advantages related to the new alloy: It can access previously unobtainable combinations of high strength, low weight and high-temperature resiliency, which is in part thanks to the additive manufacturing approach. However, energy is not the only industry that could benefit from the findings of the experiment. Aerospace researchers are constantly looking for lightweight materials that stay strong in high heat. Additionally, alloys like this could be used in the automotive industry.

The next step will be to explore whether advanced computer modeling techniques could help researchers discover more members of what could be a new class of high-performance, additive manufacturing-forward superalloys. The new model can calculate the strength of a material and make it easier to predict the performance of a new material before it is produced.

By the Editorial Board